I recently purchased the Thinkpad slice battery for my Thinkpad W520 laptop. This battery also fits the W510, T510, and T520. I noticed that when using the laptop on battery power, the slice battery would drain first followed by the regular 9 cell battery. I came into a problem where i would either nearly drain or all the way drain the slice battery (then continue on to the 9 cell) and would then suspend the laptop. The laptop would power off as it would try to draw from the dead slice battery for power even if the 9 cell had plenty of power left. If you are encountering this issue, update your BIOS to the latest version as it fixes this issue. The latest BIOS is available on lenovo’s website.